IKEA is not the only place you can get a build-your-own-furniture puzzle. If you're into the whole open source thing, there's a new repository of completely free furniture designs that are ripe for the downloadin'. The only hurdle? You have to actually make the pieces before you can put 'em together.
OpenDesk, furniture designers Joni and David Steiner and Development 00, is home to a line of completely free, completely open-source furniture that anyone can download. And if you've got your own CNC mill, you can even print out the pieces by yourself. If not, OpenDesk links in with a service called FabHub, which will help you find somebody who does.
So far, OpenDesk only has a few tables, desks, stools, so the selection is pretty limited, but the offerings will get more robust as time goes on, with any luck. Getting a whole bunch of tables milled isn't going to be the best option for everyone, but as the collection of designs grows -- and maybe starts to incorporate some weird and more niche items -- it could be a one-stop-furniture-shop for entire rooms.